An increase in team projects and an emphasis on collaboration
requires more group work and shared working space.

While office walls tumble, technologies such as speakerphone
and interactive Internet meetings are still popular.

Equipment noise is difficult to avoid in an open office setting.

Although the office of today is geared towards
cost saving, an open workspace creates the unique problem of distractions
from excessive noise. Numerous studies convincingly demonstrate that
noise is the number one contributor to lack of productivity in the
workplace. It is difficult, if not impossible, to pay attention to
details while distracting noises are prevalent.

Increased interests in the health, safety, comfort and productivity
of employees gave birth to the ergonomics boom. Acoustical concerns
in the workplace parallel, and far exceed, the trend in ergonomics.

One way to create an atmosphere that meets the needs of both the employer
and employee is to install a sound masking system. Currently, 15%
of new office buildings are equipped with masking systems and the
trend is expected to continue and expand over the next few years.

How Masking
Systems Work
Masking systems provide ambient background sound that reduces
exposure to distracting office noises by emitting a discreet,
electronically-generated sound through specially installed,
unobtrusive speakers. When installed properly, employees won't
be aware of the pink noise being generated around them, but
they will be able to focus on their work without unwanted sound
distractions. Of course, carefully choosing office furniture,
wall treatments and flooring systems will also contribute to
a productive work area.

Checklist of Masking Systems for Open Plans

Ideally, speakers should be in enclosures located just above
suspended ceilings, aimed upward toward hard plenum surfaces.
If sound absorbing insulation is applied to the underside of the
structural deck, speakers should be aimed downward (or possibly
sideways) or speaker enclosures that reflect sound downward should
be used.

Plenums should have uncomplicated air duct layouts and smooth
sound-reflecting structural surfaces to allow wider spacings between
loudspeakers.

Coverage should include adjacent areas (or zones) so occupants
moving about the building will not notice the masking system.

Masking should not exceed a sound level of 45 to 50 dBA because
occupants tend to raise voices to compensate, thus defeating the
intended masking effects. Occupants may also begin to complain
about the sound level when it exceeds 50 dBA.

To reduce the likelihood that occupants will notice background
masking, consider installation procedures that initially operate
the system at low sound levels. Then gradually increase the level
by about 1 dB each day until the desired masking level is achieved
in a week to ten days or longer.

A well-designed masking system deliberately garbles the sound
it produces and therefore should not be used for paging and routine
office functions.

Provisions can be made to reduce masking noise levels during
off-hours to enhance ability of security personnel to hear unusual
sounds.

Be sure to consider the consequences of background masking on
the usability of open plans by hearing-impaired persons. For example,
when background noise levels exceed 30 dBA, hearing-impaired persons
(even when using hearing aids) have far more difficulty understanding
speech than do normal-hearing persons.

In addition to avoiding excessive noise levels, background noise from
electronic sound masking systems in open office plans should have
a neutral tonal quality. This may be facilitated by designing the
system to simulate familiar building sounds, such as the airflow at
diffusers and registers of HVAC systems. The electronically produced
sound levels in the finished room should be no higher than necessary
to mask unwanted intruding speech and so that pronounced hisses are
avoided. The sound level of the masking system should be neither too
high nor too low, and the spectrum should roll off at the high end
of the frequency range.

In open plans, loudspeakers can usually be hidden in plenums above
suspended ceilings. This strategy can achieve uniform masking sound
throughout the room. Be careful when designing this kind of installation
because openings for return or supply air in ceilings and luminaries
can be noticeable sound leaks, which make it difficult to achieve
uniform masking sound.

Closer spacings may be required when spray-on, sound absorbing fire
protection or insulation is applied to the underside of structural
decks, or when complicated air duct layouts or deep structural members
obstruct plenums.

For more information on masking systems and to read the ASTM Standard
Guide for Open Office Acoustics (ASTM E1374-02), click
here.

For a list of other
related articles on Acoustics.com, please click here.